Flash lamp firing circuit



Oct. 21, 1952 H. 1.. MALONE El AL FLASH LAMP FIRING CIRCUIT 2SHEETS-SHEET 1 Filed Aug. 9, 1951 HAROLD L. MALONE ED6A R 5. MAR VININVENTOR.

A TTORNE Y3 Oct. 21, 1952 1 MALQNE r AL 2,614,409

FLASH LAMP FIRING CIRCUIT Filed Aug. 9, 1951 2 SHEETS SHEET 2 FIEl.E

14 FLASH HOLDER CIRCUIT EXTENSION UNIT E HAROLD L. MALONE EDGAR 6. MARVIN IN VEN TOR.

chronizer switch to fire the lamps in timed Patented Oct. 21, 1952 FLASHLAMP FIRING CIRCUIT Harold L. Malone and Edgar S. Marvin, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporationof New Jersey Application August 9, 1951, Serial No. 241,074

6 Claims.

The present invention relates to a flash holder having abattery-capacitor flash circuit into which one or more extension lampunits may be connected in series with the lamp socket of the holder, andparticularly to an extension plug in the flash holder circuit which isnormally short-circuited when no extension unit is connected thereto andwhich automatically connects a trimmer resistor into the flash holdercircuit when no extension unit is connected into the circuit, and cutsthe trimmer resistor out when an extension unit is connected into thecircuit.

Professional and press photographers are flnding it more and moredesirable or necessary to use a plurality of flash lamps inphotographing a scene, and to fire them all at one time in synchronismwith the opening of the shutter. This means that the main flash holderwhich is normally attached to the camera must contain a power sourcesufficient to fire a plurality of lamps at one time and must providemeans for selectively connecting a plurality of extension units into themain flash circuit of the holder to be ignited by said power source. Inaddition to the plurality of lamps used, it is quite common forphotographers to use a solenoid shutter vtripper which also relies onthe power source of the flash holder for its power. It has been foundthat a compact and suitable power source for this entire load can bederived from a batterycapacitor power pack wherein two 22 /2 volthearing aid type dry cells are used to charge up an electrolyticcapacitor which is then discharged through the lamps upon closure of thesynrelation with opening of the shutter.

Because of the fact that power packs of this nature put out a relativelyhigh current momentarily, i. e., 25 amperes in the circuit to bedescribed, some difliculty has been encountered in using flash holdersso powered in combination with shutters having a built-in flash switchor synchronizer. It has been found that these high currents tend to meltor pit the relatively light switch contacts used in such built-insynchronizers, and that this condition is aggravated by the fact thatthe switch contacts in this 'type of synchronizer have a tendency tobounce or vibrate at a high rate of. speed with the result that thecircuit is actually made and broken many times during the very-shortduration that the high current is flowing. It has also been foundthat'in order to fire a plurality of lamps simultaneously in a reliablefashion, the lamps should all be connected in series with one anotherand the power source rather than in parallel relation. When a flashholder is used whose circuit is designed to selectively accommodate oneor more extension units, this means that a shorting type extension plugmust be used in order that the circuit will function when one or moreextension units are not'being used.

Accordingly, the primary object of the present invention is to provide aflash holder which has a battery-capacitor power source which issufflciently powerful to ignite a plurality of flash lamps at the sametime and which permits the selective addition of one or more extensionlamp units to its power circuit in series connection without in any wayaffecting the normal operation of the circuit.

Another object is to provide a flash holder of the type described whichincludes an extension plug for connecting a built-in flash synchronizerinto the circuit in controlling relation therewith.

A further object is to provide a flash holder whose circuit is sodesigned that the resistance in the circuit is always suflicient,regardless of the number of lamps used, to prevent the output of acurrent which is so high as to injure the contacts of a built-in flashsynchronizer when used in conjunction therewith.

And yet another object is to provide a flash holder whose circuitincludes extension plugs which are connected in series with the lampsocket of the holder and which are normally short-circuited so as toleave the flash holder circuit complete when one or more extension plugsare not in use.

And a further object is to provide a flash holder of the type describedwherein the extension plugs are designed to automatically cut a trimmerresistorinto, and remove said trimmer resistor from, the .flash circuitas an extension unit is left out .oradded, respectively, to the flashholder circuit.. I

Still another object is to provide an extension plug of the typedescribed for use in a flash circuit which is simple and inexpensive-tomanufacture and, at the same time, compact and foolproof in operation.

The novelfeatures that we consider characteristic of our invention areset forth with particularity in the appended claims.Theinvention-itself,- however, both as to its organization and itsmethods of operation, together with additional objects and advantagesthereof, will best be understood from the following description whenread in connection with the accompanying drawing in which:

Fig. -1 is a vertical sectional view of one-form of flash holderconstructed in accordance with one embodiment of the present invention;

Fig. 21s a circuit diagram of the flash circuit contained in the flashholder and combined with might form a part;

Fig. 4 is a rear elevational view of the exten sion plug shown in Fig.3; and

Fig. 5 is an enlarged perspective detail of the spring contact of theextension plug removed from the plug in order to show its particularshape.

Referring now to the drawings, and particularly Fig. 1, a flash holderconstructed in accordance with the present invention may comprise agenerally cylindrical housing in which may be made of any lightmaterial, i. e., magnesium, Bakelite, etc., since it is generallymounted on the side of a camera. In the present instance, it will beassumed that the housing is made of magnesium and is electricallyconducting so that certain parts of the flash circuit will be describedas insulated therefrom. If the housing were made of Bakelite, this extrainstallation would, of course, not be necessary.

The upper end of the housing is provided with a bore in which abayonet-type lamp socket H is mounted within an insulating sleeve l2. Aconventional flash lamp L is adapted to be placed in this socket and isbacked up by a reflector l3 fixed to the housing in encircling relationwith the socket. The base contact of the lamp is adapted to engage ametal contact strap 14 fixed to the wall of the housing and insulatedtherefrom by insulation material 15. That portion of the contact strap[4 engaged by the lamp base is so formed as to be resilient, and thusprovide a good electrical contact between the same and the base of thelamp.

Also contained in the housing is the power pack for the flash circuit,said pack comprising a pair of 22 /2 volt hearing aid type dry batteriesB and a 150 mfd. electrolytic capacitor C. The batteries and capacitorare connected in series with a 2700 ohm current limiting resistor Rconnected between them, it being noted that the negative side of thecondenser is hooked to the neg ative pole of the batteries since theoperation of an electrolytic capacitor depends upon current flowingthrough the same in one direction only. As indicated, the batteries maybe supported on a partition 15" in the housing while the capacitor islocated between this partition and the bottom of the housing, and theresistor R extends through a hole in the partition. The positiveterminal of the batteries is connected to the contact strap 14 through alead [5 and the positive side of the capacitor C is connected by lead I!to an extension plug l8 onto which an extension unit E (see Fig. 2)containing an additional flash lamp L may be connected by means of aflash holder plug F. This plug [8 is in turn connected in series with asecond extension plug 18 just like it and to which a second extensionunit can be connected. This second plug I8 is then connected by lead I9to the socket l I to complete the flash circuit of the flash holder. Asshown, the extension plugs l8 and [8 (which will be described fullyhereinafter) include a male type bayonet terminal 25, into which afemale type flash holder plug on an extension unit is adapted to engagein a known manner, and which terminal is seated in a recess 20 in thewall of the housing so that the plug is protected against damageresulting from accidental blows.

Looking now at Fig. 2, it will be seen that the batteries B, resistor R,capacitor C, extension plugs 18 and I8 and lamp L are connected inseries relation in a closed loop circuit so that just as soon as a newlamp L is placed in the flash holder socket the battery starts to chargethe capacitor throughthe current-limiting resistor R. It will be notedthat just as soon as the lamps are flashed the charging circuit isbroken so that the capacitor will not start to charge again until newlamps are placed in the circuit. This automatically protects thebatteries against constant wasteful drain as would be occasioned by longwaiting periods between photographic assignments. In order for thiscircuit to function whether or not there are extension units E connectedto the extension plugs l8 and i8, these extension plugs are made so asto be automatically short-circuited when no extension unit is connectedthereto as will be fully described hereinafter. Now, in order to flashthe lamp L and any extension units connected into the circuit, thecapacitor C must be discharged through the lamps. To this end, asynchronizer switch is connected across the capacitor and lamps ahead ofthe batteries and resistor R. Assuming the synchronizer switch is onebuilt into a shutter having a pair of external terminals to which anextension cord may be connected, the housing 10 is provided with ashutter plug 2| adapted to receive a companion plug on the end of such acord. As shown in Fig. 1, this shutter plug may be one of the femalebayonet type adapted to receive a companion male plug connected to theswitch contacts in the shutter. The shell terminal of shutter plug 2| isconnected by lead 22 to the lead l6 of the flash circuit, and the centerterminal of plug 2| is connected by lead 23 into the flash circuit aheadof resistor R. Now, when the capacitor is charged and the flash switchin the shutter is closed, the capacitor discharges across the lamps andignites them.

Inasmuch as a power source of this nature is capable of producing amomentary current output as high as 25 amperes, some means must beprovided to guard against such a high current being put through built-inshutter contacts lest they be damaged or destroyed. The extension plugwhich we have designed, and which will-now be described, automaticallylimits the current flow through the circuit to a safe value and, inaddition, automatically becomes short-circuited when no extension unitis connected thereto as is required of the series connection used inthisflash circuit. Referring now to Figs. 3, 4 and 5, each of the extensionplugs 18 and I8 comprises a pair of insulating plates and 3 l, of theshape best shown in Fig. 4, spaced apart by a washer 32 of insulatingmaterial and held together by rivet 33. Fastened to the face of plate 3|by rivet 33 is a first contact 34, the lower end 35 of which is bowed toform a spring, the lower end of which is normally urged toward the left,looking at Fig. 3. This first contact is of the form best shown in Fig.5, and its extreme lower end is provided with an elongated slot 36 and apair of turned-in ears 31.

A bayonet-type male terminal 38 is staked in an aperture in plate 38 inelectrical contact with a second contact 39 disposed between the twoplates 33 and 31. This contact 39 has one end 40 extending below theplates 30 and 31 and provided with a hole 4! through which lead wiresmay be inserted to connect the plug into the flash circuit. The otherend of contact 39 is turned over as indicated at '42 and xtends into ahole 43 in plate 30 to hold the contact against rotation about terminal38. slid-ably mounted within an insulating sleeve '44 within terminal 38is a second terminal 45 which takes the form of a rod. The outer end ofthis terminal 45 is adapted to engage the center contact of a femalebayonet type connector designed to flt on terminal 38 and is enlarged asshown at 45 to limit the inward travel of the rod relative to the sleeve44. The inner end of rod 45 is provided with a circumferential groove 41which is embraced by the slotted end 36 of first contact 34. Thisconnection both physically and electrically connects contact 34 tosecond terminal 45 and the normal spring action of the bowed portion ofcontact 34 acts to move terminal to its extended position (the solidline position shown in Fig. 3). When the terminal 45 is in thisposition, as it will be when no extension unit is connected thereto, thecars 31 and the lower end of first contact 34 engage a third contact ofthe iform best shown in Fig. 4 which is riveted to the inside face ofinsulating plate 3|.

The lower end of this third contact is electri- Plug is short-circuitedthis resistor is automatically connected into the flash circuit. Thevalue of this trimmer resistor is chosen so as to limit the value ofcurrent flowing through the circuit upon discharge of the capacitor to asafe value and thereby protect the switch contacts of the flash switchbuilt into the shutter. In the present instance, we have found that a 05ohm resistor across each extension plug serves this purposesatisfactorily.

When an extension unit is connected to the extension plug, the terminal4-5 is retracted to the dotted line position of Fig. 3 and in whichposition the cars 31 on the lower end of first contact 34 are moved outof engagement with third contact 50, and the circuit is now from contact34, to terminal 45, through extension E, to second terminal 38, andthence to second contact 39 and to the line. In this condition, thetrimmer resistor 5| is automatically cut out of the circuit by theopening of the switch comprising ears 31 of first contact 34 and thirdcontact 50, and the resistance of the extension unit E is added to thecircuit and will serve the same purpose as trimmer resistor 5|, namelyto limit the peak current flowing through the shutter switch S upondischarge of the condenser to a safe value. Just as soon as an extensionunit is removed from the circuit, the switch formed by contacts 34 and50 will automatically close to short-circuit the extension plug andconnect the trimmer resistor 5| back into the circuit.

In Fig. 3 we have shown a single extension plug I8 connected into aflash circuit having all of the components included in the completecircuit oi the flash holder, as shown in Fig. 2, but arranged in aslightly different manner to emphasize the discharge circuit of thecapacitor in which the extension plug functions.

In this figure we have diagrammatically illustrated a shutter-controlledflash switch S in the circuit instead of merely a shutter plug as inFig. 2 through which such a switch is adapted to be plugged into thecircuit. Looking at Fig. 3, when the shutter switch S is closed and noextension unit is connected to extension plug l8, the current from thecapacitor C flows through shutter switch S, first contact 34, ears 31,third contact 50, trimmer resistor 5| and lamp L back to C. When anextension unit E is attached to plug ID, the second terminal 45 isshifted to the dotted-line position and ears 31 on contact 34 are movedout of engagement with third contact 50 so that current can't flowthrough the trimmer resistor 5|. Instead, current now flows from Cthrough shutter switch S, flrst contact 34, terminal 45 throughextension unit E to first terminal 38, second contact 39 and lamp Lbackto C.

When two extension plugs areused, as show at I8 and i8 in Fig. 1, thenthey are hooked in series in the flash circuit by connecting the secondcontact 39 of one with the first contact 34 of the other. If theextension unit E is provided with an extension plug I8", as indicated inFig. 2, it will be of exactly the same construction as the describedextension plugs 3 and I8 and will be'connected in series with the flashholder plug and lamp socket of the extension unit. As a result, when theextension unit E is plugged into the lamp circuit of the flash holder,the extension plug I8 will function in precisely the same manner asplugs |8 and I8 which are a part of the flash holder circuit and will,in fact, become a part of the complete flash circuit wherein all of thecomponents forming a part of the capacitor discharge circuit areconnected in series.

Although we have shown and described certain specific embodiments of ourinvention, we are fully aware that many modifications thereof arepossible. Our invention, therefore, is not to be limited to the precisedetails of construction shown and described by way of disclosure, but isintended to cover all embodiments coming within the scope of theappended claims.

Having thus described our invention, what we claim is new and desire tosecure by Letters Patent of the United States is: l

l. A flash holder-comprising in combination a housing, a lamp socket insaid holder adapted-to receive a flash lamp, a power pack in saidhousing for igniting said flash lamp and including a capacitor in serieswith said socket and a battery for charging said capacitor, an extensionplug in the wall of said housing adapted to connect a synchronizerswitch in circuit with said socket and capacitor for discharging saidcapacitor through said socket to ignite the lamp therein, a normallyshorted extension plug in the wall of said housing connected in serieswith said socket and capacitor and adapted to receive a connector forconnecting another flashlamp into the circuit of said housing in serieswith the socket therein, said extension plug including a first, contactof one polarity, a second contact of the other polarity, a third contactinsulated from the other two, a trimmer resistor connecting said secondand third contacts, a normally closed shorting switch between said firstand third contacts which automatically introduces said resistor into thelamp circuit of the housing when no extension unit is connected to saidplug, a pair of terminals electrically connected to said first andsecond contacts, respectively, adapted to physically receive saidextension connector and electrically connect the same into the circuitof the flash holder, one of said terminals movably mounted relative tosaid plug and normally moved to an extended position and adapted to beretracted when said extension connection is applied thereto, and meansoperatively connecting said movable terminal with said shorting switchwhereby said switch is allowed to close when said terminal is in itsnormal extended position and is opened by movement of said terminaltoits retractedposition. a

2. A flash holder comprising in combination a housing, a lamp socket insaid holder adapted to receive a flash lamp, a power pack in saidhousing for igniting said flash lamp, and including a capacitor, abattery and a limiting resistor connected in series with each other andsaid socket whereby said capacitor is charged only when a lamp is placedin said socket, a synchronizing switch in parallel with said capacitorand lamp socket to discharge said capacitor through said socket andignite the lamp, an extension plug connected in series with said lampsocket and in that part of the circuit through which the capacitor isdischarged and adapted to receive a connector for connecting anotherflash lamp into the lamp circuit in series with the socket of theholder, said extension plug including a contact of one polarity, asecond contact of the other polarity, a third contact insulated from theother two contacts, a trimmer resistor electrically connected betweensaid second and third contacts, a;normally closed switch between saidfirst and third contacts, a pair of terminals electrically connected tosaid first and second contacts, respectively, adapted to physicallyreceive said extension connector and electrically connect the same intothe circuit of said flash holder, one of said terminals movably mountedrelative to said plug and connected to said switch so as to open thesame when the extension connector is attached thereto, whereby when saidextension is connected into the circuit said trimmer resistor is cut outof the circuit.

3. A flash holder comprising in combination a housing, a lamp socket insaid holder adapted connected in series with said lamp socket and inthat part of thecircuit through which the capacitor is discharged andadapted to receive a connector for connecting another flash lamp intothe lamp circuit of the flash holder, said extension plug including acontact of one polarity,

a second contact of the other polarity, a third contact insulated fromthe other two contacts, a trimmer resistor electrically connectedbetween said second and third contacts, a normally closed switch betweensaid first and third contacts, a pair of terminals electricallyconnected to. said first and second contacts, respectively, adapted tophysically receive said extension connector and electrically connect thesame into the circuit of said flash holder, one of said terminalsmovably mounted relative to said plug and connected to said switch so asto open the same when the extension connector is attachedthereto,whereby when said extension is connected into the circuit said trimmerresistor is-cut out of the circuit.

An extension plug for selectively connecting an additional flash lampinto a fiash circuit including a flash larnp socket,- a capacitor and asynchronizing switch connected in series so that closing of said switchdischarges said capacitor to flash the lamps, and comprising a firstcontact and a second contact connected in said circuit in seriesrelation with said lamp socket and capacitor, a third contact insulatedfrom the other two, a trimmer resistor connected between said second andthird contacts, a pair otter-minals adapted to be physically andelectrically connected to an extension connector wired to an auxiliaryflash lamp socket, one of said terminals being stationary andelectrically connected to said second contact, the other terminal beingelectrically connected to said first contact and movable between anormally extended position and a retracted position and adapted to bemoved to its retracted position when said extension connector isphysically connected thereto, a normally closed switch between saidfirst and third contacts which short circuits said plug with saidtrimmer resistor in the circuit, and means for connecting said movableterminal to saidswitch to open said switch when the movable terminal ismoved to its retracted position, whereby the trimmer resistor isdisconnected from the circuit when an auxiliary flash lamp is addedthereto.

5. An extension plug according to -claim- ,4 characterized by the factthat said normally closed switch comprises a portion of said firstcontact deformed to provide a spring arm, the

end of which is normally urged into engagement with said third contact,the end of said arm positively connected to said movable terminal sothat the spring tensiontherein serves to move said terminal to itsextended position and retraction of the terminal moves the end of thearm from engagement with the third contact.

6. An extension plug forselectively connecting an additional flash lampinto a flash circuit including a flash lamp socket, a capacitor and asynchronizing switch connected in series so that closing of said switchdischarges said capacitor to flash the lamps, and comprising a firstcontact and a second contact connected in said circuit in seriesrelation with said lamp socket and capacitor, a third contact insulated.from the other two, a trimmer resistor connected between said secondand third contacts, a pair of terminals adapted to be physically andelectrically connected to an extension connector wired to an auxiliaryflash lamp socket, one of said terminals being stationary andelectrically connected to said second contact, the other terminal beinga plunger mounted to slide from a normally-extended position to aretracted position when said extension connector is attached thereto andhaving a circumferential groove adjacent its inner end, a portion ofsaid first contact deformed extended position and retraction of saidplunger moves the end of said arm out of engagement with said thirdcontact.

HAROLD L. MALONE. EDGAR S. NLARVIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,553,662 Marsal May 22; 19512,584,858

Dritz Feb. 5, 1952

